Heretofore, a hologram recording apparatus, which may be provided with a liquid crystal device and the like, irradiates a spatial light modulator for modulating light depending on record information to be recorded, with laser light as signal light. Particularly, in the spatial light modulator, cells are arranged planarly in a matrix so that the signal light is modulated by changing transmittance of each cell depending on the record information. Furthermore, the modulated signal light is outputted with different output angles, as a plurality of diffraction light, such as 0th-order light, or 1st-order light and so on, due to diffraction phenomenon in the cell having a fine pitch. In this case, the output angle is defined by the cell pitch, which indicates an modulation unit. Then, the signal light modulated with the spatial light modulator constructed as above and reference light not passed through the spatial light modulator are interfered on the hologram recording medium. Thereby, the recording information is recorded as a wavefront on the hologram recording medium.
An angle-multiplex type hologram recording apparatus is proposed for multiplex recording different information in the same area, by changing little by little a surface angle of the hologram recording medium relative to the reference light and the signal light, particularly during recording. In the present application, the angle of the signal light relative to the hologram recording medium surface in such an angle-multiplex type recording is referred to as a “record angle” as appropriate. Furthermore, an angle as a standard of the record angle, such as the record angle when it corresponds to a normal line of the hologram recording medium surface, is referred to as a “standard record angle”. Still further, in the present application, each record plane corresponding to each record angle is referred to as an “angle record plane”, and a record plane corresponding to the standard record angle is referred to as a “standard angle record plane”.
On the other hand, a hologram reproduction apparatus consisting a pair with the hologram recording apparatus is designed to reproduce the recorded multiplex information in the same area, by changing little by little the surface angle of the hologram recording medium relative to the reproduction illumination light. In the present application, the angle of the reproduction light relative to the hologram recording medium surface in such an angle-multiplex type reproduction is referred to as a “reproduction angle” as appropriate. Furthermore, an angle as a standard of the reproduction angle, such as the reproduction angle when it corresponds to a normal line of the hologram recording medium, is referred to as a “standard reproduction angle”.
In the angle-multiplex type hologram recording apparatus, recording to each angle record plane in the same record area are successively performed for each record angle, by changing the record angle in the maximum range with increment or decrement 0.01 degree from the standard record angle (e.g. by changing little by little in the range of 88-92 degree). Incidentally, in the present application, an area on the hologram recording medium surface onto which the signal light and the reference light are irradiated together is referred to as a “record area”. In the angle-multiplex type recording, a plurality of angle record planes such as 50 planes is recorded in the same record area.
On the other hand, in the angle-multiplex type hologram reproduction apparatus, the recorded multiplex information in the same area is reproduced for each reproduction angle, by changing little by little the reproduction angle from the standard reproduction angle in response to the record angle.
Thus, in the angle-multiplex type hologram recording apparatus and hologram reproduction apparatus, the record information can be recorded respectively on a plurality of angle record planes recorded for each record angle in the same record area, and the recorded information can be reproduced respectively. Therefore, recording density and recording capacity are expected to be remarkably increased.